The subject matter of this disclosure relates to an image reading apparatus for reading images on both sides of a document that is transported in a predetermined direction on a document transport path.
Some conventional image reading apparatuses are configured such that images on both sides of a document are read while the document is transported once onto a document transport path, as disclosed in JP 2002-182437A, for example. FIG. 1 is a cross-sectional view showing a structural overview of a conventional image reading apparatus 100. The image reading apparatus 100 is provided with a document feeding tray 101, a document discharge tray 102, a document transport path 103, an image reading unit 104, and an image reading unit 105.
The document transport path 103 extends from the document feeding tray 101 to the document discharge tray 102. A document is transported on the document transport path 103 from the document feeding tray 101 to the document discharge tray 102. The image reading unit 104 and the image reading unit 105 are opposed to the document in this order along the document transport direction on the document transport path 103. The image reading unit 104 reads an image on a first side of the document with a CCD (charge coupled device) sensor. The image reading unit 105 reads an image on a second side of the document with a CIS (contact image sensor).
Transport rollers 106 and a bent portion 107 of the document transport path 103 are arranged in this order along the document transport direction upstream of the image reading unit 104 in the document transport direction. On the other hand, a portion between the image reading unit 104 and the image reading unit 105 on the document transport path 103 is formed as a substantially straight line.
The reading resolution of the image reading unit 104 is significantly different from that of the image reading unit 105, because of the difference between their reading elements. For this reason, in the conventional image reading apparatus 100, the image resolution is significantly different between the image on the first side and the image on the second side based on the acquired image data, and thus the capability to perform two different types of image processes, namely, the image process for the image data of the first side and the image process for the image data of the second side, is necessary.
Furthermore, as contrasted with the depth of focus (about 2 mm to 3 mm) of the CCD sensor provided in the image reading unit 104, the depth of focus (about 0.5 mm to 1 mm) of the CIS provided in the image reading unit 105 is small. Thus, as shown in FIG. 2, a region 109 in which the CIS provided in the image reading unit 105 is focused is small relative to a transport region 108 in the height direction of the document transport path 103. Therefore, when the document is transported through the transport region 108 without passing through the region 109, the image based on the image data acquired by the image reading unit 105 is defocused.
As described above, the portion between the image reading unit 104 and the image reading unit 105 on the document transport path 103 is formed as a substantially straight line. For this reason, the position through which the document is transported in the transport region 108 is not constant. Accordingly, in FIG. 2, image data with high definition is acquired when the document is transported through transport position 113 or 114, but an image based on the acquired image data is defocused when the document is transported through the transport position 111 or 112, of the transport positions 111 to 114.
Furthermore, since the conventional image reading apparatus 100 has been made smaller, the image reading unit 104 provided with the CCD sensor is located close to the image reading unit 105 provided with the CIS. In addition, as described above, the document transport path 103 between the image reading unit 104 and the image reading unit 105 is formed as a substantially straight line. Therefore, light emitted from either one image reading unit of the image reading unit 104 and the image reading unit 105 travels along the document transport path 103 to be incident as stray light on the other image reading unit, and the definition of the image based on the image data acquired by the image reading unit on which the stray light is incident is degraded.
In one aspect, an image reading apparatus is provided that is capable of acquiring image data without defocusing, for example, by eliminating irregularities in document transport positions in the direction perpendicular to the face of the document at the image reading positions.
In another aspect, an image reading apparatus is provided that is capable of reading images accurately, for example, by preventing stray light from being incident.
In yet another aspect, an image reading apparatus is provided for making an image process easy after reading images.